A literature review of cancer diagnostic tests and treatments in adults with intellectual disability

Introduction

In recent years improvements in cancer care and survival in the general population have been observed Loud & Murphy (2017). Studies have emphasised the importance of regular screening and the role that this plays in the early detection of cancer (Ding et al., 2022; Miller, 2013; Whitaker, 2020). Advancements in treatment options, as well as secondary prevention and early detection, are leading to better outcomes and decreased cancer mortality rates in the general population (Ding et al., 2022; Gini et al., 2020; Jemal et al., 2010). Despite these recent developments in treatment, and the implementation of national cancer screening programmes, large gaps exist in diagnostic and treatment options between people with intellectual disability and the general population (Cuypers et al., 2024; Mahar et al., 2024).

Adults with intellectual disability have significantly lower rates of routine cancer screening and cancer is often diagnosed at more advanced stages (Horsbøl et al., 2023; Kiani et al., 2014). Some studies specifically highlight gaps that exist in national screening programmes for cancers such as breast, cervical and colorectal (Satgé et al., 2023; Sullivan et al., 2003; Swaine et al., 2014). Evidence in the intellectual disability population points towards factors such as limited screening education, distrust in healthcare providers, and challenges in providing consent, leading to limited uptake of available screening programmes and there appear to be misassumptions on women with intellectual disability not requiring cervical screening (Power et al., 2024; Swaine et al., 2014; Weise et al., 2024; Xu et al., 2017). While there are many contributing factors to these inequalities, changes in individuals' health status may go unrecognised for significantly longer because of their intellectual disability (Kiani et al., 2014). In some cases, symptoms suggestive of cancer and cancer itself go undetected, and cancers are identified at a late stage or as a cause of death in individuals with intellectual disability (Heslop et al., 2022; Mahar et al., 2024). Communicating symptoms of cancer may be difficult for individuals with an intellectual disability, and those around them may not notice signs of illness, both reasons which may contribute to a late-stage cancer diagnosis (Satgé et al., 2014). Ultimately this phenomenon, known as diagnostic overshadowing, may contribute to a decreased quality of life and the unnecessary progression of cancer, resulting in premature mortality (Mason & Scior, 2004; McMahon et al., 2024).

Although cancer is being diagnosed at more advanced stages in adults with intellectual disability, the evidence does not show that diagnosis occurs later in life (Mahar et al., 2024; Satgé et al., 2014). In a study conducted by Satgé and colleagues, the age at which individuals with intellectual disability were being diagnosed with cancer was younger than the recommended screening age for the general population with Heslop et al. (2022) and Mahar et al. (2024) reporting similar findings in England and Canada respectively. This may be an indication that adults with intellectual disability are developing cancer earlier in adulthood, and screening protocols may need to be tailored to this. Recent evidence has shown that individuals with intellectual disability were 1.6 times more likely to be diagnosed with Stage IV breast cancer and 1.44 times more likely to be diagnosed with Stage IV colorectal cancer (Mahar et al., 2024). While the reasons why they are developing late-stage cancer at earlier ages have not yet been established, studies suggest that lowering screening ages for people with intellectual disability could be beneficial for earlier diagnosis. The prognosis for cancer patients is dependent on the cancer stage at diagnosis, so a later diagnosis in patients with intellectual disability could be a key factor accounting for differences in mortality rates.

There is limited research that focuses on treatment options for individuals with intellectual disability diagnosed with cancer. Much of the published evidence are case studies based on one individual's cancer experience with no synthesis of the published evidence available (Brown, 2011; Enomoto et al., 2015). In terms of diagnostic tools, while individuals with intellectual disability may utilise the same tools as the general population, tools such as mammography, Papanicolaou tests (pap smears), and testicular examinations, remain under-utilised by the intellectual disability population (Satge et al., 2023). The existing gaps in cancer diagnosis may be from patients not receiving regular screening (Chan et al., 2022; Sullivan et al., 2003).

Although the exploration of treatments in case studies are specific to individual patients, these treatments may set a precedent that tailored treatment plans are required for the specific needs of this vulnerable population (Brown, 2011; Delany et al., 2023; Satgé et al., 2014; Sleijfer et al., 1996). Consequently, the aim of this literature review is to explore and synthesise information relating to cancer diagnostic approaches and treatment options for adults with intellectual disability and examine the barriers that prevent adults with intellectual disability from accessing both diagnostic tools and treatments.

Methods

A literature review guided by the PRISMA Extension for Scoping Review checklist was undertaken to understand the experiences of adults with intellectual disability undergoing cancer diagnostic tests and treatments. Literature reviews provide a broad, thorough critique and examination of all the evidence available on the topic and facilitate a descriptive analysis and meaningful synthesis of the current available research (Colquhoun et al., 2014).

4. Screening process

Figure 1 summarises the screening process in a PRISMA diagram. Two assessors [KS, MD] reviewed each of the articles. A third [LL or MMcM] adjudicated in cases of dispute. The initial search resulted in 10,534 publications with 3,991 duplicates removed. A title and abstract screening of 6,543 articles was completed. Then, 236 articles proceeded to full-text review. Finally, 23 articles were extracted, along with three articles from citation searching and two additional proposed articles, resulting in a total of 28 articles for inclusion in the literature review.

Figure 1. PRISMA diagram.

Results

A total of 28 articles were included in the final review. After completing the Braun and Clark thematic analysis, the four overriding themes emerged i.e. Prevention, Education, Adaptation and Ethical practice. Some overlap was observed in articles that covered multiple themes (Armin et al., 2022; Brown, 2011; Flynn et al., 2016; Sleijfer et al., 1996; Sullivan et al., 2003). The number of people with intellectual disability represented in this review was 119,909. Studies were representative of a worldwide population; USA (n=7), UK (n=6), Canada (n=5), France, Australia and Japan (n=2), and Sweden, Denmark, Taiwan and The Netherlands (n=1). Overall, 16 articles investigated preventative measures of cancer screening, seven articles discussed education on cancer and screening for people with intellectual disability, seven articles reviewed cancer treatment options for patients with intellectual disability, and three articles discussed patient autonomy, which was covered by ethical practices, see Table 4a and Table 4 in extended data. A summary of each theme’s results is provided. Screening was addressed in prevention and education. Treatments were covered by adaptation and ethical practice.

Discussion

This literature review examines the cancer diagnostic approaches and treatments available for adults with intellectual disability and any associated barriers or enablers. Results identified the importance of tailored education and application to cancer screening, diagnosis and treatment, and more involvement of adults with intellectual disability in decisions about their own care, on positive impacts on their cancer outcomes. Unique barriers to screening access were identified. Overall, the high number of individual case studies and the low numbers of people with intellectual disability in cancer studies is indicative of an under-researched area.

Although the average lifespan of people with intellectual disability has increased, as theoretically has the risk for cancer developing, they are still not receiving equitable screening to the general population (Flynn et al., 2016; Lai et al., 2014; Mahar et al., 2024; Satgé et al., 2014; Wilkinson et al., 2011).

By utilising secondary prevention, to diagnose cancer while it is still asymptomatic, cancer may be diagnosed earlier while it is still possible to have positive health outcomes (Ouellette‐Kuntz et al., 2015a). Nevertheless, individuals with intellectual disability may be unable to recognise signs and symptoms suggestive of cancer or be able to communicate their symptoms to a caregiver, and the caregiver may be unable to recognise symptoms which could make them more easily overlooked unless regular checks occur (Ouellette-Kuntz et al., 2015a).

A key risk factor for cancer is ageing, and screening for cancer detection is recommended at specific ages. Historically, the intellectual disability population had shorter lifespans, and many would not reach the age when preventative measures commenced and therefore were excluded from standard screening (Flynn et al., 2016; Lai et al., 2014; Mahar et al., 2024; Satgé et al., 2014; Wilkinson et al., 2011). However, people with intellectual disability may not receive necessary cancer screening due to a unique set of barriers (Bates & Triantafyllopoulou, 2019; Delany et al., 2023; Ouellette-Kuntz et al., 2015b).

Where people resided was identified as a barrier to screening access (Sullivan et al., 2003; Xu et al., 2017). People who lived in institutionalised care facilities had less screening levels, perhaps due to higher levels of intellectual disability and less resources at the facility (Armin et al., 2022; Sullivan et al., 2003). Additionally, if a patient lives alone in a rural environment, a geographical influence is seen where transportation to screening may be difficult, often leading to less screening attendance (Yen et al., 2014). Conversely, one study showed a protective factor for those who resided in a group home or medical facility, where they were more likely to receive cancer screening due to established policies and procedures (Xu et al., 2017).

Elevated rates of late diagnosis are reported for people with intellectual disability compared to the general population. Studies indicate that patients with intellectual disability were more likely to detect breast, colorectal, and lung cancer at stages III and IV rather than stages I or II (Mahar et al., 2024; Satgeé et al., 2023). These late-stage diagnoses of cancers meant that only limited treatments were available, and a high mortality rate occurred. Furthermore, people with intellectual disability have an onset of tumours at earlier ages than that of the general population, so normal screening timelines are inadequate for a timely diagnosis (Heslop et al., 2022; Mahar et al., 2024).

Cognitive deficits associated with intellectual disability may make understanding cancer screening procedures or communicating with relevant specialists more difficult, which can heighten stress and anxiety surrounding procedures, resulting in their cancellation (Bates & Triantafyllopoulou, 2019; Horsbøl et al., 2023; Wilkinson et al., 2011). A need for education on cancer screening was identified as critically important, to enable a person with intellectual disability to engage with screening. Many individuals with intellectual disability are not educated about the need for cancer screening or the processes involved, and often do not feel prepared to attend screening, which reduces uptake (Wilkinson et al., 2011). A lack of education and preparation has contributed to large gaps in cancer screening (Ishimaru et al., 2022). Females with intellectual disability expressed feelings of confusion, and felt they could not communicate their emotions with their providers and that their doctors did not understand the extent of their confusion (Wilkinson et al., 2011). Furthermore, patients felt they were misinformed or given inadequate information about screening procedures resulting in inadequate preparation. Results suggested that health professionals should take the time to explain to individuals with intellectual disability the specific details of procedures and provide additional support options such as videos for clarity (Sullivan et al., 2003; Wilkinson et al., 2011).

A link between higher levels of education and higher levels of screening engagement has been observed which indicates a focus on education and reasonable adjustments for people with intellectual disability is necessary to increase cancer knowledge, confidence and screening participation rates (Armin et al., 2022; Greenwood et al., 2014; Swaine et al., 2014; Wang et al., 2015; Wilson et al., 2018). While education is an important foundation for supporting patients with intellectual disability, it is crucial that this is provided in conjunction with adaptations for cancer treatments (Armin et al., 2023). Case studies have demonstrated that modified chemotherapy regimens are feasible for the successful treatment of cancer for patients with intellectual disability and concluded that following evidence-based practice is not always the best route of cancer care for individuals with intellectual disability, and that health care providers need to take time to make the necessary care adjustments (Delany et al., 2023; Enomoto et al., 2015). These case studies, while limited in numbers, demonstrated that individuals with intellectual disability should be considered for chemotherapy treatments, and providers should tailor treatment and care to their specific needs.

Radiation and surgery are often an integral part of cancer treatment. Both have been successfully adapted and employed in patients with intellectual disability, where individualised care based on the unique needs of the patients with intellectual disability was considered (Gandhidasan et al., 2020; Ishimaru et al., 2022). While there are ethical debates about men with testicular cancer undergoing radical inguinal orchidectomy for both diagnosis and treatment, the cure rate can be increased by finding an appropriate balance of therapy (Hafeez et al., 2015).

Indeed, ethical principles play a large role in the type of cancer treatment that individuals with intellectual disability receive. A case study on a stem cell transplant largely focussed on treatment ethics, although this known risky therapy was not proven to be successful because of the complications the patient experienced, independent of the presence of an intellectual disability (Brown, 2011). Similarly, studies explored debates regarding pain management and prescription drugs being used in the treatment of individuals with intellectual disability (Axmon et al., 2018; El-Tallawy et al., 2023; Millard & de Knegt, 2019; Segerlantz et al., 2019). Older adults with cancer and intellectual disability were less likely to receive prescription pain medications then their counterparts resulting in the under-management of pain and a reduction in quality of life (Segerlantz et al., 2019).

The ethical debate of treating cancer patients with intellectual disability continues into the theme of autonomy. Having an intellectual disability may inhibit an individual's understanding of a plethora of topics which may further alter how decisions are made (Hafeez et al., 2015). Nonetheless, the intellectual disability community has a long history of debating how to handle decision-making and notifying patients with intellectual disability of different diagnoses, especially when it comes to cancer, complicated by individual country legal frameworks and capacity (Delany et al., 2023; Kiani et al., 2014; Tuffrey-Wijne et al., 2010). Often people with intellectual disability have difficulties being independent and may have carers who have influence over their medical, educational, and financial decisions (Kiani et al., 2014). A lack of truth-telling stems from wanting to protect the patient from excess anxiety and distress, though it may limit the patient’s autonomy. However, there is a lack of evidence about distress after cancer diagnosis in patients with intellectual disability, implying that these patients should be entitled to honesty when it comes to their care and making medical decisions (Bernal & Tuffrey-Wijne, 2008; Flynn et al., 2016). Furthermore, medical professionals participated in non- “truth-telling” due to feelings of discomfort when working with this population, and they conferred solely with care partners about the patient's condition rather than with the patient themselves (Flynn et al., 2016; Tuffrey-Wijne et al., 2010). Studies also found evidence where carers have asked for the professionals to discuss diagnosis with the patients and the professionals refused, most likely due to a lack of confidence or understanding of intellectual disability. Brown explains an ethical dilemma where a patient who was unable to consent for themselves underwent aggressive treatment, in line with best practice, despite doubts raised by nursing staff (Brown, 2011). The patient passed away from pneumonia within a year of treatment, which brings into question the overall suitability of the treatment. Informed consent is a demonstrated successful consent method for patients with intellectual disability and should be used as part of a standard protocol. These findings may serve as a guide for healthcare professionals in providing diagnostic and treatment options, educating their patients, and communicating with patients with intellectual disability about their illness. Cancer patients with intellectual disability need to have their voices included in the research.

Conclusion

This literature review highlights substantial differences in treatment and diagnosis needs in cancer patients with intellectual disability and their general population peers. It provides evidence of the lack of research in the area where case studies dominate and the urgent need to cater for this underserved, underrepresented population. Unique barriers to screening including living conditions, age, life span and communication difficulties, contributed to later diagnosis and worse cancer outcomes.

This review demonstrates that people with intellectual disability should be provided with more education on cancer screening and treatment options and should have access to screening at earlier ages. Finally, this literature review showed that in order to preserve ethical principles, people with intellectual disability should be provided with more tailored treatment options, their autonomy should be given due consideration and truth-telling should be practiced, which could improve their cancer diagnosis and treatment outcomes.

Limitations

This literature review has several limitations including an over reliance on case studies with the heterogeneity of study designs making synthesis more challenging. Given the extensive body of literature, it is possible that some relevant studies were not included. Additionally, cancer diagnosis and treatment may have a geographical residential influence which may impact study findings. Equally, the subjective nature of thematic analysis may affect the interpretation and applicability of findings. Lastly, aged results are reported due to a dearth of recent evidence.